Thick film technology was developed in the 1960s and is widely used in many industries after several decades of development. However, the development of thick film heating technology is not long. Thick film heating elements refer to heating elements that are made by fabricating exothermic materials on a substrate into thick films and providing electricity thereto to generate heat. The conventional heating methods include electrical heated tube heating and PTC heating. Both methods adopt indirect heating. Both electrical heated tube heating and PTC heating conduct heat indirectly with low thermal efficiency, and are structurally huge and bulky. Besides, in consideration of environmental protection, heaters using these two types of heating methods stain easily after repeatedly heating and cleaning thereof is not easy. Additionally, PTC heaters contain lead and other hazardous substances and are easily oxidized, causing power attenuation and short service life.
Chinese application CN2011800393787 discloses a combination of an electrical heating element and a heat dissipator heated thereby. The heating element comprises a substrate, an insulating layer located on the substrate and a thick film conductor located on the insulating layer; wherein the second side of the metallic substrate is in contact with the heat dissipator, which comprises a layer of metallic material on a surface thereof facing the heater. The substrate is brazed to the heat dissipator, and the surface of the heating element over which the thick film conductor extends is substantially equal to the surface of the heat dissipator.
It could be seen from the above technology that the thick film technology is developing gradually; however, the thick film conductors of the above-mentioned thick film heating element are combined with the substrate through the insulating layer, instead of coated on the substrate directly. Such heating element could not transfer heat to the substrate directly when the thick film is given electricity to generate heat, which would affect the heat generating rate. Besides, the above technical solution overcomes heat dissipation problem of the thick film by utilizing external devices, but does not provide solutions in designing thick film elements of specific materials for various products to solve heat dissipation problem caused by excess heating temperature of the thick films. There are few thick film heating products that could realize direct heating, especially for situations in which heating of only a single side is required. The application of a thick film circuit for single-side heat transferring covering layer in the products to transfer heat only on one side to reduce heat loss has greatly broaden the development of heating products. The existing heating devices could meet the demands of heating; however, heating device that performs unilateral heating transfer is rarely seen, or unilateral heat transfer of such device is too poor, making it difficult to reduce heat loss by keeping high unilateral thermal conduction properties.